Add length, minLength and maxLength XSD datatype facets

lib/rdf/xsd/datatypes/string.ex

@@ -9,6 +9,25 @@ defmodule RDF.XSD.String do
     name: "string",
     id: RDF.Utils.Bootstrapping.xsd_iri("string")
 
+  def_applicable_facet RDF.XSD.Facets.MinLength
+  def_applicable_facet RDF.XSD.Facets.MaxLength
+  def_applicable_facet RDF.XSD.Facets.Length
+
+  @doc false
+  def min_length_conform?(min_length, value, _lexical) do
+    String.length(value) >= min_length
+  end
+
+  @doc false
+  def max_length_conform?(max_length, value, _lexical) do
+    String.length(value) <= max_length
+  end
+
+  @doc false
+  def length_conform?(length, value, _lexical) do
+    String.length(value) == length
+  end
+
   @impl RDF.XSD.Datatype
   @spec lexical_mapping(String.t(), Keyword.t()) :: valid_value
   def lexical_mapping(lexical, _), do: to_string(lexical)

lib/rdf/xsd/facets/length.ex

@@ -0,0 +1,3 @@
+defmodule RDF.XSD.Facets.Length do
+  use RDF.XSD.Facet, name: :length, type: integer
+end

lib/rdf/xsd/facets/max_length.ex

@@ -0,0 +1,3 @@
+defmodule RDF.XSD.Facets.MaxLength do
+  use RDF.XSD.Facet, name: :max_length, type: integer
+end

lib/rdf/xsd/facets/min_length.ex

@@ -0,0 +1,3 @@
+defmodule RDF.XSD.Facets.MinLength do
+  use RDF.XSD.Facet, name: :min_length, type: integer
+end

test/support/test_datatypes.ex

@@ -1,4 +1,13 @@
 defmodule RDF.TestDatatypes do
+  defmodule Initials do
+    use RDF.XSD.Datatype.Restriction,
+        name: "initials",
+        id: "http://example.com/initials",
+        base: RDF.XSD.String
+
+    def_facet_constraint RDF.XSD.Facets.Length, 2
+  end
+
   defmodule Age do
     use RDF.XSD.Datatype.Restriction,
         name: "age",

test/unit/xsd/datatypes/string_test.exs

@@ -3,6 +3,16 @@ defmodule RDF.XSD.StringTest do
     datatype: RDF.XSD.String,
     name: "string",
     primitive: true,
+    applicable_facets: [
+      RDF.XSD.Facets.MinLength,
+      RDF.XSD.Facets.MaxLength,
+      RDF.XSD.Facets.Length,
+    ],
+    facets: %{
+      max_length: nil,
+      min_length: nil,
+      length: nil
+    },
     valid: %{
       # input => { value, lexical, canonicalized }
       "foo" => {"foo", nil, "foo"},